Very simple and inexpensive DIY...I had a 4" gray PVC pipe in the garage. I cut it to about a foot long and placed it on the back of the sled on the back bumper. I grabbed a pair of skies and a snow board and put them on the sled in the optimal spot. Made a mark where the skis crossed it and cut a notch 3/4 the way through to accept the boards. I reinforced the slots with some U bolts and nuts to hold it in place. This came in handy because the bottom of the u bolt fit right next to the bumper and i was able to attach the contraption with some short ski straps.
This all sounds confusing. Ill take some pictures this week. It is probably $10 in parts and is very easily removable if i just want to go sled.